TOPLINE:

Once-only sigmoidoscopy screening in Norway reduced colorectal cancer (CRC) incidence by 28% and CRC mortality by 37% in men over 23 years but showed minimal benefit in women. Among men, screening reduced the 23-year cumulative risk for CRC from 6.0% to 4.3% and CRC death from 2.2% to 1.4%, whereas women experienced only modest reductions.

METHODOLOGY:

• Previous meta-analyses of four large, randomized trials demonstrated that sigmoidoscopy screening reduces CRC incidence and death over 15 years. One trial that was not strictly population-based recently reported sustained effects for 21 years; thus, the effect of sigmoidoscopy screening beyond 15 years remained uncertain.
• Researchers conducted a randomized controlled trial (NORCCAP) in Oslo and Telemark County, Norway, randomly assigning 100,210 persons aged 50-64 years without CRC to once-only sigmoidoscopy screening (with or without one fecal immunochemical test) or no screening between 1999 and 2001.
• A total of 98,654 participants were included in the intention-to-screen analyses: 20,552 in the screening group and 78,102 in the no-screening group, with screening participation rates of 61.4% in men and 64.7% in women.
• Participants with positive screening results (any polyp ≥ 10 mm, any adenoma, CRC, or positive fecal immunochemical test result) were referred for colonoscopy within 6 weeks, with 96% adherence to colonoscopy after a positive sigmoidoscopy.
• Primary outcomes included CRC incidence and CRC death, with follow-up through national registries until December 31, 2023, resulting in a median follow-up of 22.5 years for both outcomes.
• Researchers estimated age-standardized cumulative risks at 23 years using weighted Kaplan-Meier curves and calculated hazard ratios (HRs) using Cox proportional hazards models stratified by age group (50-54 and 55-64 years).

TAKEAWAY:

• In men, the 23-year cumulative risk for CRC was 4.3% vs 6.0% in the screening group vs the no-screening group, with a risk difference of -1.7 percentage points (HR, 0.72).
• In women, the 23-year cumulative risk for CRC was 4.2% vs 4.7% in the screening group vs the no-screening group, with a risk difference of -0.5 percentage points (HR, 0.89; 95% CI, 0.80-0.997; P for heterogeneity between men and women = .007).
• For CRC death in men, the 23-year cumulative risk was 1.4% vs 2.2% in the screening group vs the no-screening group, with a risk difference of -0.8 percentage points (HR, 0.63).
• In women, no statistically significant reduction in CRC death was observed, with a 23-year cumulative risk of 1.3% vs 1.4% in the screening group vs the no-screening group (risk difference, -0.1 percentage points; HR, 0.97; P for heterogeneity between men and women = .004).

IN PRACTICE:

“Offering sigmoidoscopy screening in Norway reduced CRC incidence more in men than in women and reduced CRC death only in men,” wrote the authors of the study.

SOURCE:

The study was led by Edoardo Botteri, PhD, Cancer Registry of Norway, Norwegian Institute of Public Health, and Øyvind Holme, MD, PhD, Research Unit, Sørlandet Hospital Trust, Kristiansand, and Clinical Effectiveness Research Group, University of Oslo, Oslo, Norway. It was published online on May 12 in Annals of Internal Medicine.

LIMITATIONS:

The study design presented challenges including different invitation-to-control ratios between age groups (1:3 vs 1:5.4 for those aged 55-64 years vs 50-54 years) and study sites, which required appropriate statistical adjustments. Complete data on opportunistic screening use throughout the follow-up period were unavailable, though data from 2009 to 2016 showed 14.2% of invitees and 12.1% of control participants had a colonoscopy, indicating minimal difference between groups. The study had reduced statistical power for sex-specific analyses, and because randomization was conducted in the overall cohort rather than within sex strata, exchangeability within sex-specific subgroups cannot be formally guaranteed. Follow-up relied on national registries rather than direct patient contact.

DISCLOSURES:

The study received support from the Norwegian government and the Norwegian Cancer Society. The authors reported having no relevant conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.